“Penicillin allergy is the most common drug allergy. It isn't clear why some people develop penicillin allergy while others don't. Prevention focuses on awareness. Treating an allergic reaction may require taking medications or, in the case of a serious reaction, emergency care. The most serious allergic reaction to penicillin is an anaphylactic response, which can be deadly. Anaphylactic reactions develop immediately after penicillin exposure in highly sensitive people and cause the airways (bronchi) to constrict, making it difficult to breathe. Blood pressure may drop to life-threatening levels, making you feel dizzy or causing you to lose consciousness. Other serious signs and symptoms include:

• Wheezing
• Lightheadedness
• Slurred speech
• Rapid or weak pulse
• Blueness of your skin, including your lips and nail beds
• Diarrhea
• Nausea and vomiting

Seek emergency medical care if you think you or someone else is having an anaphylactic reaction.” Source: Mayoclinic.com